Adaptive sampling region for a region editing tool

ABSTRACT

Properties of pixels in a digital image are sampled within different subdivisions of an editing tool impression to produce different property distributions. The different subdivisions can automatically alter their size, geometry, and/or location, based on image content within one or more of the subdivisions, in order to encompass a set of pixels having a substantially uniform distribution of a pixel property. Uniformity can be defined relative to the editing operation or context of the image. The property distributions from each region are classified to identify different edit classes within the property space, which are then used to apply an edit effect to the digital image within the tool impression. The edit classes may be represented by an edit profile in two or more dimensions.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent Ser. No.10/781,572, entitled “Adaptive Region Editing Tool”, filed Feb. 17, 2004and incorporated herein by reference for all that it discloses andteaches.

TECHNICAL FIELD

The invention relates generally to image editing, and more particularlyto an image region editing tool.

DESCRIPTION

Digital image editing has made many sophisticated graphics andmultimedia editing capabilities accessible to a large number ofprofessionals and consumers. Users can edit digital images, such asphotographs, video frames, computer graphics, etc., usingreasonably-priced image editing software. Such software can execute on avariety of computers, including graphics workstations, desktopcomputers, and laptop computers. However, depending on the user'sabilities, some of these sophisticated editing capabilities may stillpresent tasks that are too complex or too time-consuming for many usersto perform with acceptable results.

One common image editing operation involves the selective editing of aregion in the image. For example, given a still digital image (e.g., adigital photograph or a video frame) of a human subject, a user may wishto remove (e.g., erase) the background in the image (e.g., an officeenvironment) and replace it with a different background (e.g., a beachscene). In one approach, region erasure of the background can beaccomplished manually, pixel-by-pixel, by changing the color and/oropacity of each pixel of the background. However, not only can thisapproach be tedious and very time-consuming, manually determining theappropriate color and translucence of each pixel on the boundary betweenthe subject and the background can be quite complicated. First, it canbe difficult to correctly identify which pixels are actually in thehuman subject and which pixels are in the background, particularly whenthe subject has a complex shape or very fine attributes. Furthermore,some pixels include a blend of both subject and background and,therefore, may require some manual “unblending” of colors from thesubject and the background to produce a satisfactory result. However,manual unblending can be extremely difficult and often unworkable formany users. Accordingly, the effort required to employ a manual approachmay be unacceptable for the quality of the result achieved.

Some more automated approaches for editing a region can be used. Forexample, to erase a background around a subject in an image, a user maydesignate a clipping path that generally distinguishes the subject fromthe background. The region designated outside the clipping path iserased, and the boundary of the clipped region can be blurred or blendedto substantially minimize the influence of the remaining background onthe clipped subject. Although this clipping approach is less manual thana pixel-by-pixel approach, the approach typically relies on a userspecifying the clipping path closely around the boundary of the subjectin order to achieved acceptable results. The more background thatremains in the clipped subject, the more influence the remainingbackground has on the resulting edited image—an undesirable effect.Furthermore, such blending or blurring tends to decrease the sharpnessof the subject boundary, even though sharpness is frequently a primarydesirable characteristic.

Other approaches employ automated visual blending techniques that do notrequire clipping. However, such existing approaches define an individualerasure color based on analysis of a single region of a tool impression.These approaches fail to take sufficient advantage of the instructiveeffort of a user, who is capable of communicating useful informationabout different regions within a tool impression simply by his or herplacement of the tool within the image. Furthermore, while instructiveuser input is helpful, existing editing tools do not adequately optimizetheir sampling geometry based on image region content to provideenhanced results.

Implementations described and claimed herein sample properties of pixelsin a digital image within different subdivisions of an editing toolimpression to produce different property distributions. In oneimplementation, the subdivisions are differently located within the toolimpression. The property distributions from these subdivisions areclassified to identify different edit classes within the property space,which are then used to apply an edit effect to the digital image withinthe tool impression.

At least one of the subdivisions of the tool impression may be used tosample pixel properties in order to edit some of the pixels within thetool impression. In some implementations, the sampling region mayautomatically alter in size, geometry, and/or location based on imagecontent within the sampling region. Such alterations may be controlledby a sampling criterion, such as a uniformity metric, a standarddeviation, a sampling trend criterion, and other statistical andnon-statistical parameters.

In some implementations, articles of manufacture are provided ascomputer program products. One implementation of a computer programproduct provides a computer program storage medium readable by acomputer system and encoding a computer program. Another implementationof a computer program product may be provided in a computer data signalembodied in a carrier wave by a computing system and encoding thecomputer program.

The computer program product encodes a computer program for executing acomputer process on a computer system. Pixels in a first region within atool impression in a digital image are sampled to determine a firstdistribution of a pixel property of the pixels in the first region. Thefirst region within the tool impression is modified to encompass a setof additional pixels within the tool impression. A second distributionof the pixel property is determined based on the pixels in the modifiedfirst region. Pixels in a second region within the tool impression aresampled to determine a third distribution of the pixel property of thepixels in the second region. At least one pixel within the toolimpression is edited based on the second and third distributions.

In another implementation, a method is provided. Pixels in a firstregion within a tool impression in a digital image are sampled todetermine a first distribution of a pixel property of the pixels in thefirst region. The first region within the tool impression is modified toencompass a set of additional pixels within the tool impression. Asecond distribution of the pixel property is determined based on thepixels in the modified first region. Pixels in a second region withinthe tool impression are sampled to determine a third distribution of thepixel property of the pixels in the second region. At least one pixelwithin the tool impression is edited based on the second and thirddistributions.

In yet another implementation, a system is provided. A region samplingmodule samples pixels in a first region within a tool impression in adigital image to determine a first distribution of a pixel property ofthe pixels in the first region. The region sampling module also samplespixels in a second region within the tool impression to determine asecond distribution of the pixel property of the pixels in the secondregion. An adaptive sampling region module modifies the first regionwithin the tool impression to encompass a set of additional pixelswithin the tool impression and determines a third distribution of thepixel property based on the pixels in the modified first region. Anediting module edits at least one pixel within the tool impression basedon the second and third distributions.

In yet another implementation, a system includes means for samplingpixels in a first region within a tool impression in a digital image todetermine a first distribution of a pixel property of the pixels in thefirst region, means for modifying the first region within the toolimpression to encompass a set of additional pixels within the toolimpression, means for determining a second distribution of the pixelproperty based on the pixels in the modified first region, means forsampling pixels in a second region within the tool impression todetermine a third distribution of the pixel property of the pixels inthe second region, and means for editing at least one pixel within thetool impression based on the second and third distributions.

Other implementations are also described and recited herein.

FIG. 1 illustrates a screenshot of a region editing tool employing anadaptive sampling region.

FIG. 2 illustrates exemplary relationships among a tool impression on adigital image, region property distributions, and two edit profiles.

FIG. 3 illustrates block encoding artifacts in a digital image.

FIG. 4 illustrates an exemplary erasure of a background of a digitalimage using a perfect uniformity criterion.

FIG. 5 illustrates an exemplary erasure of a background of a digitalimage using a near-uniformity criterion and a static-sized samplingregion.

FIG. 6 illustrates an exemplary erasure of a background of a digitalimage using a near-uniformity criterion and an adaptively-sized samplingregion.

FIG. 7 illustrates an iterative process for adapting a sampling regionin an exemplary region editing tool.

FIG. 8 illustrates exemplary operations for region editing using anadaptive sampling region.

FIG. 9 illustrates an exemplary architecture of a region editing toolemploying an adaptive sampling region.

FIG. 10 illustrates a red-eye correction operation implemented using anadaptive sampling region.

FIG. 11 illustrates an exemplary system useful for implementing animplementation of the described subject matter.

FIG. 12 illustrates a different exemplary modification of samplingregion.

FIG. 13 illustrates an exemplary erasure of a heavily texturedbackground of a digital image using a static-sized sampling region.

FIG. 14 illustrates an exemplary sampling trend in an adaptive samplingregion application.

FIG. 15 illustrates an exemplary erasure of a heavily texturedbackground of a digital image using a sampling trend criterion and anadaptively-sized sampling region.

FIG. 16 illustrates a different exemplary sampling trend in an adaptivesampling region application.

FIG. 17 illustrates an exemplary blurring of a background of a digitalimage using a different sampling trend criterion and an adaptively-sizedsampling region.

An exemplary adaptive region editing tool samples one or more properties(e.g., colors, texture) of pixels in a digital image within differentsubdivisions of an editing tool impression to produce different propertydistributions. Generally, an editing tool combines an image regiondesignation, typically via a user interface, and an editing operation.In one implementation, the image region designation (e.g., a toolimpression) can be automatically altered based on image region contentwithin the region. An editing brush or wand represents an exemplaryediting tool. The property distributions from each region are analyzedto identify different edit classes within the property space. Thedifferent edit classes are then used to apply an edit effect to thedigital image within the tool impression (e.g., modifying hue propertyvalues of individual pixels, replacing one color with another, erasingpixels having a given color or being within a given color range, etc.).The edit classes may be represented by an edit profile in two or moredimensions (e.g., applying to one or more pixel properties).

Adaptive editing involves altering an editable property of a pixel andmay include without limitation background erasure, red-eye correction,retouching, masking, surface normal processing, modifying image effects,blurring, sharpening, adjusting contrast, and labeling of image areasand features. In one implementation, the image region designationincludes a sampling region centered within the tool impression, althoughin other implementations, the sampling region can be located anywherewithin the image. Depending on image region content (e.g., if the imageis uniform or nearly uniform within the sampling region), the samplingregion can increase in size or alter in shape or location until thesampled image region content violates a specified sampling criterion. Inthis manner, the sampling region can expand or change to optimize theimage content sampled in the region editing operation.

It should be understood that “uniformity” of pixel properties may havean absolute sense but may also be understood to have a relative sense inrelation to the editing task the tool performs. For example, athreshold, range or limit defining the uniformity of the color variationin a sample region will be smaller when the task merely requiresinclusion of block compression artifacts in the sample than when thetask necessitates removal of shades of all red during red-eyecorrection. In turn, the permitted variability will, for example, beeven larger when the task is the erasure of a strongly textured imagebackground. As such, “uniformity” specifies a range of permittedvariability, which may be relative to a given editing operation, imagecontext, or user perception.

Furthermore, the uniformity of pixel properties in a sample may bedescribed in any convenient way, for example using statisticaldescriptions. In an exemplary implementation, uniformity is defined as aratio of variability within a pixel property distribution to a measureof central tendency of the distribution. Exemplary measures of centraltendency include without limitation the mean, the median or the mode ofthe distribution. Examples of measures of variability may includewithout limitation standard deviations and variances of thedistribution. An example of a preferred ratio describing uniformity isthe coefficient of variation, which is the ratio of the standarddeviation of the distribution to its mean.

It is common for a user to wish to erase a background of a digital image(e.g., to replace an original background with a different background).If the background is perfectly uniform (e.g., in a blue screen setting)and the foreground is sufficiently different, it is possible to discernwhich pixels in a given region are background and which are foregroundusing a zero-tolerance color similarity test. However, in anothersituation, a region may be “nearly uniform”, in that it contains variouspixel properties (e.g., colors) that are mathematically distinct but sovisually similar that the region itself would still be treated by a useras a single type of region (e.g., the background). In yet anothersituation, a region may be significantly textured (e.g., a patternedbackground), but still be treated by a user as a single type of region.

In some circumstances, the sampling region of a tool impression may bemodified during an editing operation according to image content, therebyproviding improved results over existing methods. In one respect, thisfeature is related to the concept of Just Noticeable Difference (JND)between colors. It is possible to numerically define colors in a colorspace between which a user can perceive no difference because thenumerical differences are smaller than the JND. The range of colors thatappear identical to the user (i.e., that are just short of the JND)should be edited in the region, even if the colors differ numericallywhen expressed in some color space. Likewise, it is possible to define arange of colors and textures that user considers to be sufficientlysimilar that they represent features of a designated image region (e.g.,a patterned background).

For example, a color distribution within a central sampling region canbe sampled. Then, the central sampling region can be modified (e.g.,grown, re-shaped, or relocated) to capture other pixels in the imageregion that exhibit a similar color property. Such sampling regionadaptation can improve the ability of the editing tool to edit imagefeatures perceived by the user to be similar enough to receive the sameediting treatment.

FIG. 1 illustrates a screenshot 100 of an exemplary region editing toolemploying an adaptive sampling region. An image window 102 contains aview of a digital image 104. Selection of a background erasure toolbutton 106 initiates the exemplary region editing tool. Operation of theexemplary tool is characterized by display of a tool impression 108around the tool symbol 110 in the illustrated implementation. In oneimplementation, the tool impression 108 defines the portions of thedigital image 104 to be analyzed during a region editing operation. Thetool impression 108 may also be manipulated by the user within thedigital image display, such as by use of a keyboard, mouse, stylus, orother input device. Manipulation may include without limitation changesin location, size, shape, and orientation.

In FIG. 1, the tool impression 108 is illustrated as a circular region,although other shapes may be employed, including without limitationsquare regions, rectangular regions, and adjustable regions. Theillustrated tool impression 108 defines two component regions: asampling region 112, and an outer region between the sampling region 112and the outer boundary of the tool impression 108. Furthermore, invarious implementations, the dotted line boundary of the sampling region112 may or may not be visible to the user. In alternativeimplementations, tool impression regions and component regions of othershapes and orientation may be employed, including rectangular regions,triangular regions, regions of different shapes, adjacent regions (asopposed to concentric), overlapping regions, and non-adjacent regions.In addition, more than two subdivision regions may be employed.

In the illustrated implementation, the sampling region 112 defines aregion from which the region editing tool extracts pixel properties usedin determining editing parameters. While the size, shape, location, andorientation of the sampling region may be held static during an editingoperation, in alternative implementations, the characteristics of thesampling region may be adaptively altered during an editing operation.For example, given a sampling region of an initial size, the region canbe grown to encompass additional pixels within the tool impression. Inthis manner, the image content sampled in the sampling region can beoptimized toward a particular objective, as discussed below.

In one implementation, the sampling region may be dynamically sizedbased on the values of pixel properties found in the tool impression orin individual subdivisions of the tool impression. For example, the sizeof a round sampling region may be automatically set by incrementallyincreasing the radius of a round sampling region until the width of acolor difference distribution of pixels in the sampling region increasesbeyond a given threshold width, which might suggest that the samplingregion has grown to include a portion of the object's color. Otherapproaches for dynamically adapting the size, shape, location, andorientation of the component regions based on image content are alsocontemplated.

The individual subdivisions allow a user to provide intelligent guidancefor the selection of how and whether an individual pixel is edited. Forexample, as discussed, a user may wish to erase the background of animage, leaving the human subject (i.e., the foreground object)unchanged. In the illustration of FIG. 1, the tool impression 108 isplaced in the digital image 104 so as to erase the pixels comprising thesky while leaving the pixels comprising balloon and basket relativelyunchanged. Accordingly, the user can communicate guidance for thisselection to the tool by including in the sampling region 112 onlypixels to be erased and including in the outer region some pixels of theobject. Given this region-based information, the tool can then discernthrough classification which pixels to edit and how to edit them. Thisclassification may be aided by the adaptive alteration of the samplingregion 112.

Examples of editing may include without limitation modifyingimage-related pixel properties, such as color, transparency, etc., butmay also include modifying existing non-image-related pixel propertiesor adding additional properties (e.g., labels or properties applied tocertain areas of the digital image). Various pixel properties and colorspaces may also be employed, singly or in combination, in otherimplementations, including CMYK, Lab, and other color space values, aswell as transparency, brightness, hue, and saturation. Furthermore,non-image pixel properties are also suitable, including a membershipassociated with a pixel, a feature vector (e.g., a texture descriptor ora color histogram of an image region), a height map, a depth map in ascene, a displacement vector, etc.

It should also be understood that different color spaces may be used forthe individual adaptive editing sub-operations, including determiningcomponent region characteristics, determining an edit profile,performing the edit, and generating display characteristics. Forexample, the edit profile may be based on color distributions in theregions while the editing operation may perform a “selectiverestoration” action in which a previously executed editing operation isselectively “undone” (e.g., by performing a generally opposite editingaction) according to the edit profile. In this manner, aspects of theimage region may be selectively restored to a previous state (i.e., byselectively undoing a previously executed fill operation).

In the illustrated implementation, the appearance of a pixel ischaracterized by at least four values: three color channel values (e.g.,red, blue, and green or RGB) and an opacity (or conversely,transparency) channel value, which defines the opacity of the pixel. Thecolor channel values may be combined in a variety of ways to represent asingle color selected from a given color space. The opacity channelvalue represents a degree by which an object obscures another objectbeneath it. For example, an object with 100% opacity completely concealsan object beneath it. In contrast, an object with 0% opacity iscompletely transparent and allows an object beneath it to be totallyunobscured. An object with an opacity value between 0% and 100% ispartially transparent. Specifically, the opacity of an object is definedby the opacity of the individual pixels that comprise it. (In FIG. 1,the checkerboard pattern visible in the image represents a region ofpixels exhibiting some level of transparency.)

Accordingly, the exemplary adaptive editing tool of FIG. 1 analyzespixel properties within each of the component regions of its toolimpression to determine pixel property distributions within eachcomponent region. For example, in the illustrated tool example, thecolors of each pixel (or of some subset of individual pixels) within thesampling region 112 are identified. In addition, the colors of pixelswithin the outer region are sampled. From these pixel color samples, theediting tool computes pixel color distributions associated with eachregion. It should be understood that property distributions may bequantized to any chosen degree and may represent, without limitation,frequencies of pixels having given property values, an integration ofsuch frequencies, or some other mathematical derivation of the propertyfrequencies. In addition, in some implementations, propertydistributions may be represented by histograms or hierarchies.

Sampling a pixel generally refers to the process of reading a pixelproperty for the purpose of analysis or classification. Furthermore, apixel property may include an overall image, object or region propertythat is associated with a given pixel (e.g., an object label). Samplingmay also be performed on all pixels in a given region or on arepresentative fraction of the pixels in the region, which may beconsidered sparse sampling.

Given the pixel property distributions of the multiple component regionsin the tool impression, the tool determines edit classes in the pixelproperty space (e.g., the color space) to which an editing effect may beassigned. For example, edit classes may be specified as: (1) an ErasureClass—a class of colors to be completely erased; (2) a Partial ErasureClass—a class of colors to be partially erased; and (3) an UnchangedClass—a class of colors to be left unchanged. However, in alternativeimplementations, it should be understood that any number of classes andediting effects may be controlled by the edit profile.

In the illustrated example, each pixel within the tool impression 110 isclassified into one or more defined edit classes based on the pixelproperty value associated with the pixel. In some implementations, thedefined edit classes may model classified pixel property distributionswithin a tool impression or may be derived from such classified pixelproperty distributions (e.g., computed based on a mathematical transformof the distributions). In one implementation, the editing effects areassigned to individual edit classes by way of an edit profile, asdiscussed with regard to FIG. 2. In alternative implementations,multiple editing effects may also be combined in more than one editclass (e.g., as a result of overlapping edit classes), or edit classesand membership therein may be determined by a probability function, soas to provide somewhat fuzzy or non-discrete edit class boundaries inthe property space.

Accordingly, an edit profile may be used to apply one edit effect to oneedit class of pixels within the image and a different edit effect toanother edit class of pixels. In contrast, multiple edit effects formultiple edit classes are also contemplated. An edit effect may modifyone pixel property of one edit class and the same or different pixelproperty of a second edit class. The pixel property being modified maybe the same as or different from that used to segregate pixels into editclasses. The transition between different edit effects may be abrupt orgradual, with some pixels receiving an intermediate effect. Pixelsreceiving an intermediate effect may be of a separate edit class or mayrepresent regions of overlap of class probability or class membership.The edit profile may determine an effect to be applied in absoluteterms, for instance by prescribing a new value for a pixel property toreplace the old, such that the new value (i.e., a replacement value)depends solely on the profile. The edit profile may also designatevalues of a new pixel property not previously associated with pixelswithin the image. Alternatively, the edit profile may represent amathematical transformation between old and new property values of apixel, such that the resulting image property depends both on the editprofile and on the original pixel property value. For instance, the editprofile may represent a scaling factor for an existing image property.More complex transformations are also contemplated wherein the new pixelproperty is expressed as a parameterized function of the originalproperty with parameter values determined by the value of the editprofile.

In the illustrated example, erasure may be accomplished by setting theopacity channel values of pixels within the tool impression 110 havingcolor values within the erasure class to 0% opacity, setting the opacitychannel values of pixels within the tool impression 110 having colorvalues within the partial erasure class to some value between 0% and100%, and setting the opacity channel values of pixels within the toolimpression 110 having color values within the unchanged class to 100%opacity. (In one implementation, the opacity channel value of each pixelis scaled, not merely set, between 0% and 100% original opacity of thepixel in accordance with the edit profile, in order to accommodatepixels already having a non-zero opacity.) Alternatively, transparencymay be scaled by a scaling factor derived from the edit profile.Furthermore, the edit profile may set the allowable extremes of theediting effect to factors different than 0% and 100%. As previouslynoted, erasure is only one example of the type of editing that may beselectively performed using implementations described herein.

In an alternative implementation, no pixel is set to 0% opacity (or 100%transparency) during the editing operation. Instead, some pixels may beset to some low opacity level (e.g., 6%) or some high transparency level(e.g., 94%). However, as pixels exhibit such nearly complete erasureunnoticed by the user, they may be post-processed after completion ofthe editing operation to exhibit complete erasure.

FIG. 2 illustrates exemplary relationships among a tool impression 200on a digital image 202, region property distributions 204, and two editprofiles 206 and 208. The digital image 202 includes an object 210(representing a general class of pixels that are not to be edited) and abackground 212 (representing a general class of pixels that are to beedited). Both the object 210 and background 212 may include multiplecolors, textures, opacity values, etc. The adaptive region editing toolevaluates the pixel properties within the tool impression 200 todetermine how to edit the pixels therein. In one implementation, theuser places the tool impression 200 such that the outer region includespixels of the object 210 (see region portion 214) and the samplingregion 216 includes pixels of the background 212 but substantially noneof the pixels of the object 210 to guide the selective editing operationof the tool. In alternative implementations, the tool impression 200need not include any portion of the object. For example, an adaptiveretouch tool can selectively modify pixels corresponding to an editclass in the outer sampling region or selectively modify pixelscorresponding to the edit class in the sampling region, in each case thepixels in the remaining edit class(es) being substantially unchanged.

The sampling region 216 is adapted according to the image content withinthe tool impression 200. In one implementation, this adaptation is aniterative process in which the pixels within the sampling region 216 aresampled, the sampling results are evaluated (e.g., compared to asampling criterion), and if the sampling criterion is met, the samplingregion 216 is grown and the processes restarts. When the criterion isviolated, the size of the sampling region 216 returns to a smaller sizethat does meet the sampling criterion.

In an alternative implementation, only the pixels newly encompassed bythe modified sampling region are sampled and compared to the originalsampling region distribution. These pixels are said to lie within an“incremental modification region”, which may also encompass new pixelsby virtue of a shape change, a translation, a rotation, a hardnesschange, etc. For example, if the width of the pixel propertydistribution of the newly encompassed pixels exceeds the width of thepixel property distribution of the original sampling region by thesampling criterion, the growth of the region will stop and the regionwill revert back to a size that will not violate the sampling criterion.

When the adapted sample region size is achieved, the properties ofpixels within the sampling region 216 are analyzed to produce a pixelproperty distribution 218, and the properties of pixels within the outerregion are sampled to produce a pixel property distribution 220. In FIG.2, the vertical axis of distributions 204 represents the number orfraction of pixels having a pixel property value. The sampled propertyvalues are likely to be distributed throughout each region. For example,if the pixel property is color (or a color difference), it is reasonableto expect that the various pixels might exhibit some distribution ofcolor throughout each region.

It should be understood, however, that although this description of FIG.2 relates to a single type of property (e.g., color) for each pixel,multiple properties may also be sampled to produce distributions ofmultiple properties for each pixel, such as values of multiple colorchannels, opacity, texture, etc. A given property, such as color, mayhave one or more dimensions. For example, color represented by an indexinto a color palette could be considered as one-dimensional because asingle number—the palette index—is sufficient to define it.Alternatively, color defined by an RGB triplet of a pixel isthree-dimensional, one dimension for each of red, green and blue.However, a pixel property may also be composite. For example, a givenpixel may be associated with several numbers representing texture insome way and some values representing color. Therefore, a pixel propertymay represent at least: (1) a one-dimensional single property, (2) amulti-dimensional single property, or (3) a composite property.

In one implementation, a distribution of pixel properties of pixels inthe sampling region is analyzed. An exemplary pixel property that may beemployed in this analysis involves the color difference between thecolor of the pixel at the center of the sampling region 216 and thecolor of each other pixel in the sampling region 216. The backgroundcolor CB (comprising of the color components RB, GB, and BB) is taken tobe the color or the center pixel of the sampling region 216. The colorCB may be used to establish the origin for the color difference axis andmay be used for unblending pixels containing colors of both the objectand the background. It should be understood that the color CB may alsobe computed using other algorithms, such as an average or median or modecolor of pixels in the sampling region. (A vector median or mode returnssome color that actually exists in the image.)

Differences in pixel properties, including multidimensional properties,may be computed in a variety of ways dictated by the nature of theintended editing operation. Distance Dist in p property space ofdimension i may be expressed as a Minkowski sum or b norm:

${Dist} = \left\lbrack {\sum\limits_{i}\left( {p_{i} - p_{i\; 0}} \right)^{b}} \right\rbrack^{1b}$where p_(i( )) is a reference property value relative to whichdifferences are computed. This reference property value may, forexample, represent a background color. The exponent b may have a varietyof integer or non-integer values (e.g., 1, 2, or 4). When b is 1, for avector valued property p_(i), such as color represented by R, G and B,Dist is equivalent to a simple sum:Dist=(R−R ₀)+(G−G ₀)+(B−B ₀)

-   -   For b=2, Dist is computed as the Euclidean distance:        Dist=√{square root over ((R−R ₀)²+(G−G ₀)²+(B−B ₀)²)}{square        root over ((R−R ₀)²+(G−G ₀)²+(B−B ₀)²)}{square root over ((R−R        ₀)²+(G−G ₀)²+(B−B ₀)²)}

Distances may be computed with regard to sign, or using absolute valuesas in a Manhattan distance:Dist=|R−R ₀ |+|G−G ₀ |+|B−B ₀|

Distance calculations may also take into account property distributions(e.g., by means of a Mahalanobis distance). Furthermore, distances maybe computed along individual property dimensions i, or subsets of thesedimensions, and then combined into a single metric by mathematicaltransformation. For example, a minimum value may be selected:Dist=MIN(|R−R ₀ |, |G−G ₀ |, |B−B ₀|)or a weighted combination value may be derived:Dist=w _(R)(R−R ₀)+w _(G)(G−G ₀)+w _(B)(B−B ₀)wherein w_(i) represents the weight for the contribution of a propertyor property dimension i. Additionally, one subset of property dimensionsmay be treated differently from another as in:Dist=MAX(|R−R ₀ |, |G−G ₀|)+|B−B ₀|

Distances along individual dimensions may be combined into a singlemetric by rule, including the use of conditional rules as, for example,in:Dist=MAX(|R−R ₀ |,|G−G ₀|)+|B−B ₀| if Sign(R−R ₀)=Sign(G−G ₀)≠Sign(B−B₀)Dist=MAX(|G−G ₀ |,|B−B ₀|)+|R−R ₀| if Sign(G−G ₀)=Sign(B−B ₀)≠Sign(R−R₀)Dist=MAX(|B−B ₀ |,|R−R ₀|)+|G−G ₀| if Sign(B−B ₀)=Sign(R−R ₀)≠Sign(G−G₀)

Depending on editing needs, it may be advantageous to form a metric fromonly a subset of pixel properties or only from a subset of pixelproperty dimensions. In one implementation pertaining to a prototypicalvector p_(i) in a property space of dimension i=4, a distance may beexpressed for example as:Dist=[(p ₁ −p ₁₀)^(b)+(p ₃ −p ₃₀)^(b)+(p ₄ −p ₄₀)^(b)]^(]b)

Properties may also be transformed from one representation to anotherbefore computing a distance. For example, a color vector may betransformed to an opponent color representation such as L*a*b* or intoan approximately opponent representation such as:RGB=(R+G+B)/3RG=(R−G+256)/2BY=(2B−R−G+512)/4

After such a transformation either all or some of the properties orproperty components may be used to compute a property difference. Forexample, an approximately lightness-independent color difference may beestimated using:Dist=|RG−RG ₀ |+|BY−BY ₀|or:Dist=√{square root over ((RG−RG ₀)²+(BY−BY ₀)²)}{square root over((RG−RG ₀)²+(BY−BY ₀)²)}

It should be understood that when a distance is estimated for acomposite pixel property, such as combination of color and texture, theform of the metric for each component property may be chosenindependently and the metrics may be combined with different weights orby independent rules.

When using multidimensional property spaces, especially spaces of highdimension, it may be beneficial to include dimensionality reduction inthe estimation of a distance in property space. Such dimensionalityreduction may, for example, be achieved by employing only the leading orleading few principal components of the space. Alternatively,discriminant axes may be determined by a method such as linear or Fisherdiscriminant analysis. It is also possible to use principal componentanalysis in combination with discriminant analysis to discardinsignificant property component vectors and then select a mostdiscriminating vector from the remaining components. In yet anotherimplementation, distributions may be fitted using mixture models, whichmay then be used to classify properties of the image.

A result of the described sampling operation in the sampling region is apixel property distribution, such as is represented by distribution 218.Likewise, the outer region is also sampled to produce an outer regionpixel property distribution 220. Other methods of determining pixelproperty distributions (e.g., color difference distributions) may beemployed.

For an exemplary classification used in an adaptive background eraser, athree-dimensional color space has been converted into one-dimensionaldistance measurements. However, it is also possible to achieve thisdimensionality reduction in other ways. First, dimensionality may bereduced by using only the leading principal components of the pixelcolors under the tool impression. Secondly, one or more discriminantaxes may be selected using, for example, linear discriminant analysis.The Principal Component Analysis step and the Linear DiscriminantAnalysis step can also be combined.

As seen in distributions 204, the distributions associated with the tworegions (i.e., the sampling region 216 and the outer region of the toolimpression 200) overlap considerably. In the illustrated example, thisis to be expected in that the outer region includes a large area thatcontains background pixels. However, other distribution combinations arealso possible, including combinations in which the sampling and outerregion do not overlap, combinations in which multiple modes exist(whether the distributions overlap or not), etc. A variety ofdistributions are shown in examples in later Figures.

Accordingly, a feature of the exemplary tool is to take advantage of theuser's placement of the tool impression regions to discern an editprofile based on the property distributions within the two differentlylocated regions. In one implementation, it is assumed that the propertydistribution of pixels in the sampling region 216 represents theproperties that are to be edited. It is also assumed that the propertydistribution of pixels in the outer region includes some properties thatare not to be edited. These two assumptions facilitate theclassification of properties values into distinct edit classes. Itshould be understood, however, that the editing may be in the inversesense.

In one implementation, the edit profile is determined throughclassification of the property distributions to identify properties indifferent edit classes. In an example of an adaptive background erasuretool, Alpha (or “transparency”) values may be derived according to ameasure of similarity between the color of a pixel under the brush andan estimate of the background color under the brush. In oneimplementation, pixels having colors that are very similar are fullyerased (set to 100% transparency), whereas pixels having colors that arevery different are not erased (no change to the transparency of thepixels). Intermediate color differences result in a partial erasure bychanging the transparency of a pixel to some intermediate Alphavalue—the greater the color difference, the greater the change in theintermediate Alpha value. In another implementation, no pixels arecompletely erased, although complete erasure may be achieved at a latertime through post processing.

As shown in the edit profile 206, the pixel property range from theorigin to parameter T₁ represents a first edit class (in this example,generally representing the background), the range between parameter T₁and parameter T₂ represents a second edit class (in this example,generally representing a probable mix of background and object), and therange greater than parameter T₂ represents a third edit class (in thisexample, generally representing the object).

In computing the example of edit profile 206, parameters characterizingthe two pixel property distributions are computed. In oneimplementation, the mean color difference of the backgrounddistribution, MeanB and the variance of the background distribution,VarB, are computed for determining the minimum tolerance parameter T₁.When Var_(B)/Mean_(B) exceeds a threshold Thresh_(B), T₁ may be computedas:T ₁ =k×√{square root over (Var_(B))}

-   -   where k is a constant inversely proportional to the Sharpness        setting. If threshold Thresh_(B) is not exceeded, the sampling        region may be iteratively expanded by a one-pixel wide contour        about its periphery until this threshold is reached. Then T₁ may        be estimated as before or as:        T ₁ =k×Integ        where Integ is the color difference at a fixed fraction of the        integral of the difference distribution, such as 90% for        instance.

Once the minimum tolerance parameter T₁ is computed based on the pixelproperty distribution in the sampling region 216 of the tool impression200, the pixel properties under the outer region of the tool impression200 are analyzed to determine the maximum tolerance parameter T₂. Thepixels within this region are characterized by an unknown combination ofpixel properties (e.g., of object and background colors). The pixelproperty distribution 220 for this region is filtered to exclude allpixels having pixel properties below the minimum tolerance parameter T₁.In one implementation, the mean color difference of the objectdistribution, Mean_(O), and the variance of the object distribution,Var_(O), are computed for determining the maximum tolerance parameterT₂. Up to a predefined magnitude of k, T₂ may be taken as:T ₂ =k×MIN(Mean_(O),√{square root over (Var_(O))})and above this magnitude as:T ₂ =k×√{square root over (Var_(O))}

If Var_(B)/Mean_(B) is less than the threshold Thresh_(B), the value ofT₂ may be adjusted as follows:T ₂ =T ₁ +T ₂

Additionally, when Var_(O)/Mean_(O) is less than a threshold,Thresh_(O), but √{square root over (Var_(O))} exceeds a secondthreshold, ThreshV_(O), the same adjustment may be performed. Ingeneral, T₁ and T₂ are constrained to represent non-null colordifference ranges and to lie within their respective data ranges, andthe value of T₁ is further constrained to be less than that of T₂.

Other types of classification may be employed to define editing classes.For example, more conservative values of thresholds may be used, i.e. aminimum tolerance T₁ and a maximum tolerance T₂ to define edit classesof colors that have a very high probability of belonging to thebackground and the object respectively. These two conservative editclasses may be used as training sets for a classifier that categorizesthe remaining colors.

Alternatively, any of several probability density functions may befitted to the pixel property distribution of the sampling region. Bysubtraction of the extrapolated distribution of the color differences inthe outer region of the brush, a better estimate of true object colorsmay be obtained to act as a training set. Suitable exemplary trialdistributions include without limitation the normal, binomial, Poisson,gamma and Weibull distributions. Additional exemplary distributions maybe found in the Probability distribution section of Wikipedia(http://en.wikipedia.org/wiki/Probability_distribution). Suchdistributions may also be used for classification using Bayesianstatistics. Because of the projection of color differences onto a singleaxis, several distinct colors may have color differences falling in asingle histogram bin. The original colors contributing to each bin canbe identified in the three-dimensional color space and the training setmember colors can be used for a classification of colors inthree-dimensional space.

Exemplary methods for suitable for this classification are described inT.-S. Lim, W.-Y. Loh and Y.-S. Shih, “A Comparison of PredictionAccuracy, Complexity, and Training Time of Thirty-three Old and NewClassification Algorithms”, Machine Learning Journal, vol. 40, p.203-229, 2000, and include categories such as decision tree approaches,rule-based classifiers, belief networks, neural networks, fuzzy &neuro-fuzzy systems, genetic algorithms, statistical classifiers,artificial intelligence systems and nearest neighbor methods. Thesetechniques may employ methodologies such as principal componentanalysis, support vector machines, discriminant analysis, clustering,vector quantization, self-organizing networks and the like.

As an alternative to this form of classification, the colordistributions of the sampling region and the outer region may be treatedas two signals to be separated into background and object categories bythe techniques of blind signal separation. Since the sampling regionprovides a background signal not significantly contaminated by objectcolors, this represents a more straightforward case of semi-blind signalrecovery. An element of blind signal separation is the use of higherorder statistical measures. Suitable methods for blind signal separationare described in J.-F. Cardoso, “Blind signal separation; statisticalprinciples”, Proc. IEEE, vol. 9(10), p. 2009-2025, 1998 and in A.Mansour, A. K. Barros and N. Ohnishi, “Blind Separation of Sources:Methods, Assumptions and Applications”, IEICE Trans. Fundamentals, vol.E83-A, p. 1498-1512, 2000.

The edit profile relates an editing effect, designated θ, to thedifferent edit classes. For example, in an erasure operation, theediting effect may represent a transparency value (i.e., the inverse ofopacity). As such, edit profile 206 specifies a nearly 100% transparencyvalue for the edit class between 0 and parameter T₁, representingcomplete erasure of pixels having colors falling in this range. Forexample, the transparency may range from about 99% at a color differenceof zero to about 92% at parameter T₁. In contrast, the edit profilespecifies an unchanged transparency value for the edit class greaterthan parameter T₂, representing no change to the pixels having colorsfalling in this range. For pixels having colors falling betweenparameter T₁ and parameter T₂, edit profile 206 specifies a roughlylinear scaling of the transparency effect (e.g., transparency changedecreases with increasing color differences).

It should also be understood that although the edit profiles of FIG. 2are shown to be based on a single pixel property distribution, editprofiles may also be generated for multiple pixel properties andtherefore are not limited to two dimensions.

In alternative implementations, an edit profile need not be based onsharp thresholds, as shown by the sigmoidal edit profile 208, where aparameter can define a point of inflection or any other feature of anedit profile based on a pixel property. For example, the parameters T₁and T₂ may be employed to define an edit profile that defines an Alphavalue (i.e., defining transparency of a pixel) based on the tildefunction:Alpha=1−exp{−T ₁[ln(DIFF_(max)/DIFF)]^(T) ² }where DIFF represents the color difference of a pixel under the toolimpression, DIFF_(max) represents the maximum DIFF value of all pixelsunder the tool impression, and T₁ and T₂ are the parameters.

Sigmoidal functions may also be used, including without limitation thearctangent and the tangent functions, and an adaptation of the Weibullfunction, with the form:Alpha=1−exp[−(T ₂/DIFF)^(T) ¹ ].

Other exemplary sigmoidal functions that may be adapted to define editprofiles are listed below:

${\bullet\mspace{14mu}{Alpha}} = {{1 - \left( {\frac{2}{\left( {1 + {\mathbb{e}}^{- {(\frac{DIFF}{s})}}} \right)} - 1} \right)} = \frac{2{\mathbb{e}}^{- {(\frac{DIFF}{s})}}}{\left( {1 + {\mathbb{e}}^{- {(\frac{DIFF}{s})}}} \right)}}$${\bullet\mspace{14mu}{Alpha}} = {1 - \frac{sDIFF}{\sqrt{1 + {s^{2}{DIFF}^{2}}}}}$The parameter s defining these functions may be, for example, derived bycentering the point of inflection between the parameters T₁ and T₂ andmatching the slope of the line between the parameters T₁ and T₂.

In an alternative implementation, one or more thresholds are omittedfrom definition of the edit profile. Instead, the edit profile isdefined by inflection points, decay constants, or other functionalparameters. In this manner, the editing operation may be tuned to moreeffectively implement the user's desired editing effect. The methods ofdefining these functional parameters may be similar to those used indefining the thresholds discussed above.

FIG. 3 illustrates exemplary artifacts in a digital image 300. Theartifacts 302 in FIG. 3 are the result of block encoding in a lossycompression operation (e.g., JPEG encoding). The artifacts 302 are moreapparent in the exploded view 304. From the view 304 of digital image300, the artifact regions would likely be treated by a user as part ofthe background to be erased, even though the artifact regions 302include colors that are mathematically different than the chosenbackground color.

However, as shown below, such artifacts can corrupt the results of someediting methods. A result of a zero tolerance editing method based oncolor similarity with a single sampled edit color is shown in a digitalimage 400 of FIG. 4. In the implementation shown in FIG. 4, the editingoperation is a color replacement operation in which the sampled color isreplaced with white. If a pixel's color does not equal the edit color,the pixel is not edited. As such, this method will not edit a pixelcontaining an artifact because the pixel color is not exactly the samecolor as the edit color. Accordingly, the non-uniform pixels of thebackground are not edited.

Digital image view 500 of FIG. 5 shows the result of an adaptive editingoperation on the original digital image 300 of FIG. 3 using anon-optimized sampling region 502 and an edit profile generatedtherefrom. In the illustrated implementation, the fixed square samplingregion 502 of 12 by 12 pixels is located within a tool impression (notshown) and is specifically positioned to encompass only the uniform greybackground shown in FIG. 3. (In FIG. 5, the location of the samplingregion 502 is shown relative to the digital image after the editingoperation has been completed.)

The color differences under the sampling region 502 are calculated andcompared to a preset color difference threshold. However, as shown, thesampling region 502 encompasses only a uniform grey region and does notencompass any of the artifact regions 504. Therefore, the edit profileis set according to the grey region only. For example, in FIG. 5, thethreshold for complete erasing is set to a color difference of 1, byvirtue of the complete uniformity of the sampled pixels. As such, theediting operation fails to adequately remove certain colors in theartifact regions in the background. Accordingly, although the adaptiveerasure operation may have improved the erasure results over that ofFIG. 4, the results are still unacceptable.

Digital image view 600 of FIG. 6 shows the result of an adaptive editingoperation on the original digital image 300 of FIG. 3 using an adaptivesampling region 602 and an edit profile generated therefrom. Adifference between the sampling region 502 of FIG. 5 and the samplingregion 602 is that is that the size of the sampling region 602 has beenincreased to the point that portions of the artifact regions have beenencompassed by the sampling region 602. The resulting size of thesampling region 602 is 40 by 40 pixels. The increase is the result of anadaptation performed by the editing tool, in which the sampling region602 is increased until the uniformity of the sampled pixels degrades toa given threshold by virtue of encountering the object or otherwiseencountering sufficiently differently colored pixels.

Because the optimized sampling region 602 expanded to encompass portionsof the artifact regions, the sampled pixel property distribution withinthe sampling region 602 reflects the contribution of the artifactpixels. As such, the resulting edit profile is adapted to edit a largenumber of the artifact pixels. By comparison to FIG. 5, a threshold (orsome other functional parameter) for complete erasing is set in FIG. 6to 27 by virtue of the contribution of the artifact pixels encompassedby the larger sampling region. By comparing the views in FIGS. 5 and 6,it is clear that the adapted edit profile more accurately edits thepixels that the user would consider nearly uniform and part of thebackground.

FIG. 7 illustrates an iterative process for adapting a sampling regionin an exemplary region editing tool. A digital image region 700 includesseveral foreground objects (i.e., the balloons), which represent ageneral class of pixels that are not to be edited, and a background(i.e. the sky, which represents a general class of pixels that are to beedited. Both the foreground objects and the background may includemultiple colors, textures, opacity values, etc. However, in theillustrated implementation, the background possesses a uniform orsubstantially uniform color distribution, which allows the adaptiveregion editing tool to adapt the sampling region in order to optimizethe edit classification operation.

In one implementation, the user places a tool impression 702 such that aouter tool impression region includes pixels of the foreground objectsand a central sampling region 704 includes pixels of the background, butsubstantially none of the pixels of the foreground objects, in order toguide the selective editing operation of the tool. A distribution graph706 depicts an exemplary pixel property distribution 708 associated withthe set of pixels encompassed by the sampling region 704 and anexemplary pixel property distribution 710 associated with the set ofpixels residing in the outer region, between the periphery of thesampling region 704 and the periphery of the tool impression 702. Notethat the portion of the outer region distribution 710 that overlaps thedistribution 708 of the sampling region overwhelms the distribution 708.

Based on the sample taken from the central sampling region 704, the tooldetermines that the sampled background region is sufficiently uniform towarrant adaptation of the sampling region. To determine sufficientuniformity of a sampling region in one implementation, the tool computesthe mean color difference of the background distribution, Mean_(B) andthe variance of the background distribution, Var_(B). If the ratio of

$\frac{{Var}_{B}}{{Mean}_{B}} \leq T_{Uniform}$where T_(Uniform) represents a threshold of sufficient uniformity (e.g.,2.5 in one implementation), then the sampling region is deemedsufficiently uniform for adaptation. The T_(Uniform) parameter may behard-coded into the tool, derived from analysis of exemplary imagedatabases, software-settable (e.g., based on image content analysis) bysome other means or user-settable, depending on the desired features ofthe tool.

Having deemed the sampling region to be sufficiently uniform foradaptation, the tool modifies the sampling region by altering the size,shape, location and/or orientation of the sampling region. In thedigital image region 712, the sampling region is shown to have grownuniformly (e.g., the radius about the center of the circular sampleregion 704 has increased) to produce a modified sampling region 714. Themodified sampling region is sampled and evaluated relative to athreshold of sufficient uniformity (such as T_(Uniform) or some otherparameter). While the modified sampling region is deemed to besufficiently uniform, the sampling region is re-modified, re-sampled,and re-tested in incremental stages, as shown in digital image regions716 and 718. However, when the uniformity of the incrementally modifiedsampling region falls below the applicable threshold of sufficientuniformity, as shown in digital image region 718 (i.e., the samplingregion overlaps pixels of the foreground objects), the modified sampleregion reverts to a previous sample region having sufficient uniformity,as shown in digital image region 716.

As previously discussed, the comparison to the sampling criterion may bebased on pixels within the sampling region or on some combination of theoriginal sampling region and the pixels that are newly encompassed bythe modified sampling region. Other comparisons are also contemplated,such that the editing tool is able to discern whether the newconfiguration of its sampling region has violated a sampling criterion,wherein the sampling criterion is set to optimally apply editing effectsto pixels perceived by the user to be essentially in the same type ofregion.

Accordingly, the sampling has been enhanced to include additional pixelshaving sufficiently similar pixel properties to have captured a moreaccurate sample of the set of pixels to be edited (e.g., the backgroundpixels). Likewise, the outer region sample contains fewer pixels sharingsimilar pixel properties with pixels that are to be edited. Therefore,as is shown by the pixel property distribution graph 720, a result ofthe sampling region adaptation is that the uniform sampling region(e.g., “background”) distribution 722 is amplified and broadenedslightly, and the overlapping portion of the outer region distribution724 is reduced. Given this modified distribution set, classification ofpixels to be edited, pixels to be partially edited, and pixels not to beedited may be altered to more accurately apply the editing effect tothose pixels perceived by the user to be essentially in the same type ofregion.

As shown in FIG. 7, one implementation modifies the sampling region byuniformly increasing the area of the sampling region (e.g., uniformlyincreasing the radius of a circular sampling region about the center ofthe region, increasing the side lengths of a square sampling regionabout the center of the region, etc.). The incremental increases may beof any viable magnitude, such as increasing the sampling regionperiphery pixel-by-pixel or by multiple pixels. However, non-uniformmodifications are also contemplated as shown in FIG. 12.

FIG. 8 illustrates exemplary operations for region editing using anadaptive sampling region. A definition operation 801 determines adefault edit profile, which may be applied if the definition operation816 is not executed. A detection operation 802 detects selection of atool impression relative to a digital image. The selection defines atleast a first region (e.g., a central sampling region within the toolimpression) and a second region (e.g., an outer region within the toolimpression) within the tool impression. It should also be understoodthat FIG. 8 generally describes sequential processing for an individualtool impression, but that the same sequence of operations may be appliedafter selection of multiple tool impressions, such that an aggregatetool impression with an aggregate first region and an aggregate secondregion are processed. In addition, the sampling region is not limited tobeing “central” or “circular”, but may have a variety of shapes andlocations.

A sampling operation 804 determines a property distribution for pixelswithin the first region. For example, for each pixel, a color differencevalue (e.g., relative to a reference color value) may be used as thepixel property, although other properties may be employed. An adaptiveoperation 806 modifies the first region (e.g., its shape, size,location, orientation, hardness, etc.). A second sampling operation 808determines a property distribution for all pixels within the modifiedfirst region (or for those pixels newly encompassed by the modifiedfirst region). If the property distribution of these pixels is deemed tobe to violate the sampling criterion, as determined by decisionoperation 810, the modified first region reverts back to a modifiedfirst region that satisfies the sampling criterion, in reversionoperation 812.

In contrast, if the decision operation 810 determines that the propertydistribution of the pixels satisfies the sampling criterion, anotherdecision operation 811 determines whether the modified search region hasreached a predefined limit of growth. In one implementation, this limitis the size of the tool impression, although other limits are definableas well. If the limit has been met, it means that the pixel propertiesof the entire tool impression satisfy the sampling criterion. Forexample, this can occur if the tool impression does not include anyportion of the object. In such case, the tool may not have a secondregion to consider. As such, the processing merely proceeds to anediting operation 818 and edits the pixels within the tool impression inaccordance with the default edit profile set in operation 801.

If the predefined limit of growth has not yet been satisfied, theprocessing loops back to the adaptive operation 806. As discussed withregard to FIG. 7, in one implementation, uniformity characteristics ofthe distribution of the first region are compared to a uniformitythreshold, although alternative sampling criteria are also contemplated.

Resuming the case where the sampling criterion has been violated,another sampling operation 814 determines a property distribution forpixels within the second region (which may or may not have been modifiedfrom the original second region by modification of the first region). Aclassification operation 816 defines an edit profile based on the pixelproperty distributions within the first and second regions.

The edit profile specifies the editing effects to be applied to pixelshaving properties in a given edit class. Accordingly, an editingoperation 818 edits the pixels within the tool impression in accordancewith the edit profile. For example, pixels in the erasure region mayhave their transparency values set to 100% (or to some high transparencyvalue) while pixels in the partial erasure region may have theirtransparency values set to some value between 100% and 0% in accordancewith the edit profile.

In one implementation, operations 806, 808, 810, and 812 are performedby an adaptive sampling region module 920 of FIG. 9, although otherimplementations may architect the region editing tool to support anadaptive sampling region in an alternative configuration.

FIG. 9 illustrates an exemplary architecture of a region editing tool900 employing an adaptive sampling region. In various implementations,modules may be structured as hardware or as software executing within acomputer system. A digital image 902 may be represented by encoded data,such as in JPEG format, GIF format, or some other standard orproprietary format. The digital image 902 may be received from apersistent storage medium 904 (e.g., a magnetic or optical storage disk,or flash memory) or from a communications network 906 (e.g., theInternet or a local area network). The digital image 902 is transferredto another storage medium, such as memory 908 for access by the editingtool 900.

A user interface 910 can access the digital image 902 from the memory908 and display it to a user. For example, FIG. 1 illustrates a userinterface screenshot of an exemplary region editing tool. The userinterface 910 may also receive input from the user, relative to thedigital image, instructing that assorted editing operations be performedon an area of the digital image 902 as well as parameters for suchoperations, such as the location and dimensions of the tool impression.

The input is received by an impression definition module 912, whichaccesses the memory resident representation of the digital image 902,and communicates the location and dimensions of the tool impressions aswell as the two or more subdivisions (i.e., component regions) therein.The subdivisions are differently located within the tool impression andtherefore have at least one pixel difference between them. In oneimplementation, this impression definition occurs for each toolimpression, whereas in other implementations, this impression definitionmay be applied to multiple tool impressions (e.g., to multiple distincttool impressions or to a stroke of the tool impression across the image,which is interpreted as multiple individual tool impressions). For suchaggregate tool impressions, first and second component regions may bedetermined in a variety of ways. One example is that tool impressionregions that overlap a sampling (e.g., background) component region ofany tool impression in the set are considered sampling component regionswhile all other tool impression regions are considered foregroundcomponent regions.

A region sampler module 914 samples the properties of the pixels in eachregion to produce a property distribution for each region. If anadaptive sampling region is employed, an adaptive sampling region module920 interacts with the region sampler module 914 to iterate to a moreoptimal sampling region.

An edit profile definition module 916 classifies the propertydistributions of the regions to determine a number of edit classes towhich an editing effect is applied differently. Given the edit classes,an editing module 918 applies the edit classes to individual pixelswithin the tool impression. Therefore, using the region erasure example,pixels having property values falling into the erasure class have theirtransparency values set to 100% (or some high transparency value),pixels having properties values falling into the partial erasure classhave their transparency values set to a tapered value between 100% and0%, and pixels having properties values falling into the unchanged classhave their transparency values unchanged. The editing changes are savedto memory, from which the user interface 910 can retrieve the updateddigital image data and display the changes to the user.

FIG. 10 illustrates a red-eye correction operation implemented using anadaptive sampling region. In image 1000, the pupil 1002 appearsunnaturally red from the reflection of a photographic flash or otherlight source. Using an adaptive sampling region, the user's placement ofthe tool impression 1004 and the associated sampling region 1006 may beimprecise, because the sampling region can expand, move, and otherwiseadapt to sample the other similar pixels in the red region of the pupil.A result in which the editing operation replaces the edit region with adark natural pupil color is shown in image 1008.

FIG. 11 depicts an exemplary general purpose computer capable ofexecuting a program product. One operating environment in which thedescribed system is potentially useful involves the general purposecomputer, such as shown as computer 1113. In such a system, data andprogram files may be input to the computer, including without limitationby means of a removable or non-removable storage medium or a data signalpropagated on a carrier wave (e.g., data packets over a communicationnetwork). The computer 1113 may be a conventional computer, adistributed computer, or any other type of computing device.

The computer 1113 can read data and program files, and execute theprograms and access the data stored in the files. Some of the elementsof an exemplary general purpose computer are shown in FIG. 11, wherein aprocessor 1101 is shown having an input/output (I/O) section 1102, atleast one processing unit 1103 (e.g., a microprocessor ormicrocontroller), and a memory section 1104. The memory section 1104 mayalso be referred to as simply the memory, and may include withoutlimitation read only memory (ROM) and random access memory (RAM).

A basic input/output system (BIOS), containing the basic routines thathelp to transfer information between elements within the computer 1113,such as during start-up, is stored in memory 1104. The describedcomputer program product may optionally be implemented in softwaremodules, hardware modules, or firmware loaded in memory 1104 and/orstored on a configured CD-ROM 1108 or storage unit 1109, therebytransforming the computer system in FIG. 11 to a special purpose machinefor implementing the described system.

The I/O section 1102 is connected to keyboard 1105, display unit 1106,disk storage unit 1109, and disk drive unit 1107, typically by means ofa system or peripheral bus (not shown). The system bus may be any ofseveral types of bus structures including a memory bus or memorycontroller, a peripheral bus, and a local bus using any of a variety ofbus architectures.

Generally, in contemporary systems, the disk drive unit 1107 is a CD-ROMdrive unit capable of reading the CD-ROM medium 1108, which typicallycontains programs 1110 and data. Computer program products containingmechanisms to effectuate the systems and methods in accordance with thepresent invention may reside in the memory section 1104, on a diskstorage unit 1109, or on the CD-ROM medium 1108 of such a system.Alternatively, disk drive unit 1107 may be replaced or supplemented by afloppy drive unit, a tape drive unit, or other storage medium driveunit. The network adapter 1111 is capable of connecting the computersystem to a network via the network link 1112.

The drives and their associated computer-readable media providenonvolatile storage of computer-readable instructions, data structures,program modules and other data for the computer 1113. It should beappreciated by those skilled in the art that any type ofcomputer-readable media which can store data that is accessible by acomputer, such as magnetic cassettes, flash memory cards, digital videodisks, random access memories (RAMs), read only memories (ROMs), and thelike, may be used in the exemplary operating environment.

The computer 1113 may operate in a networked environment using logicalconnections to one or more remote computers. These logical connectionsare achieved by a communication device 1111 (e.g., such as a networkadapter or modem) coupled to or incorporated as a part of the computer1113; the described system is not limited to a particular type ofcommunications device. Exemplary logical connections include withoutlimitation a local-area network (LAN) and a wide-area network (WAN).Such networking environments are commonplace in office networks,enterprise-wide computer networks, intranets and the Internet, which areall exemplary types of networks.

In an exemplary implementation, an impression definition module, aregion sampler module, an edit profile definition generator, an adaptivesampling region module, an adaptive sampling region module, and anediting module may be incorporated as part of the operating system,application programs, or other program modules executed by the CPU 1103.The digital image, the property distributions, thresholds, editprofiles, and edit classes may be stored as program data in memorysection 1104, on a disk storage unit 1109, or on the CD-ROM medium 1108.

FIG. 12 illustrates a different exemplary modification of a samplingregion. A digital image region 1200 includes several foreground objects(i.e., the balloons), which represent a general class of pixels that arenot to be edited, and a background (i.e. the sky, which represents ageneral class of pixels that are to be edited. Both the foregroundobjects and the background may include multiple colors, textures,opacity values, etc. However, in the illustrated implementation, thebackground possesses a uniform or substantially uniform colordistribution, which allows the adaptive region editing tool to adapt thesampling region in order to optimize the edit classification operation.

In one implementation, the user places a tool impression 1202 such thatan outer tool impression region includes pixels of the foregroundobjects and a central sampling region 1204 includes pixels of thebackground, but substantially none of the pixels of the foregroundobjects, in order to guide the selective editing operation of the tool.A distribution graph 1206 depicts an exemplary pixel propertydistribution 1208 associated with the set of pixels encompassed by thesampling region 1204 and an exemplary pixel property distribution 1210associated with the set of pixels residing in the outer region, betweenthe periphery of the sampling region 1204 and the periphery of the toolimpression 1202.

In contrast to the implementation illustrated in FIG. 7, the incrementalmodifications to the sampling region 1204 are not uniform and mayinclude without limitation size-changes, shape-changes, translation(e.g., moving the center of the sampling region within the image), andorientation changes (e.g., rotation of the sampling region relative tothe axes of the image). As shown in FIG. 12, the resulting modifiedsampling region 1212 in digital image region 1214 has expanded toencompass all of the contiguous pixels within the tool impression 1216sharing substantially uniform pixel properties (in this case, colors).Expansion of region 1214 may be implemented, for example, as a floodfill operation in which pixels are added conditionally based on theirsatisfaction of a sampling criterion.

Therefore, in a manner similar to that of FIG. 7, a pixel propertydistribution graph 1218 associated with the modified sampling region1212 shows that, as a result of the sampling region adaptation, thepixel properties of the uniform sampling region (e.g., “background”)distribution 1220 are amplified and the overlapping portion of the outerregion distribution 1222 is reduced, both effects being more significantthan those in the example shown in FIG. 7. Again, given this modifieddistribution set, classification of pixels to be edited, pixels to bepartially edited, and pixels not to be edited may simplified, andpotentially may be more accurate. On the basis of this classificationoperation, an edit profile can be defined and the appropriate pixels canbe edited by the adaptive region editing tool.

FIG. 13 illustrates an exemplary erasure of a heavily texturedbackground of a digital image using a near-uniformity sampling criterionand an adaptively-sized sampling region. Some image regions exhibit atexture so non-uniform that a simple near-uniformity sampling criterionwill not produce acceptable results. For example, image 1300 exhibits aheavily textured background of green foliage, dark shadows, and brownstems. However, the extremely non-uniform nature of the pixels under thesampling region 1302 results in too narrow of a full-editclassification. Accordingly, the edited image 1300 shows unacceptableresults.

FIG. 14 illustrates an exemplary sampling trend 1400 in an adaptivesampling region application. By evaluating the standard deviation ofcolor differences in the sampling region as the sampling region grows,an abrupt change in the trend may be detected at a side length of 66pixels. In one implementation, the abrupt change can be detected bycomparing the standard deviation difference between two adjacent orpredetermined sampling region sizes to a given sampling trend criterion(a specific type of sampling criterion pertaining to trend analyses).

The variation or dispersion of the pixel properties within a sampleregion may be characterized in a variety of ways, either in a relativeor absolute sense. Examples of absolute measures of variability include,but are not limited to, property range, interquartile range, meanabsolute deviation, variance, standard deviation or average entropy.

FIG. 15 illustrates an exemplary erasure of a heavily texturedbackground of a digital image 1500 using a sampling trend criterion andan adaptively-sized sampling region. The optimized sampling region sizeof 66 pixels per side leads to a broader full-edit class in the editprofile, thereby yielding a more intuitive result in which thebackground foliage is more accurately edited.

Other methods of determining an optimal sampling region size that isadaptive to image content are also contemplated. As discussed, thestatistical analysis need not be confined simply to the entire samplingregion. Instead the statistics inside the sampling region may becompared to those within a region of growth around the original orprevious sampling region. This adaptation procedure may also beiterative, wherein the previous sampling region and incrementalmodification region are combined prior to modifying the sampling regionin the next iteration. In some cases, analysis of the incrementalmodification region may facilitate detection of an abrupt change bylimiting the change analysis to incremental portions of the image.

Other statistical measures than standard deviation may be used. Forexample, the trend in a uniformity measure, such as color differencevariance divided by mean color difference, may be used. Alternatively,the color distribution or smoothed distribution within the toolimpression may be analyzed in more detail, such as by use of ahistogram, including differential and integral histograms. Thedistribution may also be represented by means of mixture models.

More generally, classifiers of various types or clustering methods maybe used to characterize the content under the tool impression. In thecase of a brush tool, where individual impressions within a stroke maybe updated as they are applied, it is preferred to use simple analysismethods for speed and responsiveness of the tool. However, more complexmethods may also be used, for example, when the result of processing isdrawn upon completion of the stroke and not during the stroke. Invarious implementations, it may also be sufficient for the adaptivesampling region methods to provide merely a sampling region that isimproved over the original sampling region (e.g., an improved samplingregion that is more characteristic of the background region intended bythe user).

As previously discussed, it should be understood that the imageproperties being analyzed and edited are not limited to color. They mayinclude other properties, such as transparency, or they may includeexplicit feature vectors that characterize, for instance, texture oranother spatial property.

It should also be understood that the method of determining edit classesunder the tool impression may be chosen independently of the criteriaused to determine an improved size of a sample region. For example, thethreshold for erasure may be chosen according to standard deviation ofcolor differences as opposed to color range within the sample, while thesampling region size may be determined using a uniformity metric.

FIG. 16 illustrates a different exemplary sampling trend 1600 in anadaptive sampling region application. By evaluating a uniformity metric(e.g., color difference variance/mean color difference) in the samplingregion as the sampling region grows, an abrupt change in the samplingtrend 1600 may be detected at a side length of 114 pixels. In oneimplementation, the abrupt change can be detected by comparing theuniformity metric difference between two adjacent or predeterminedsampling region sizes to a given sampling trend criterion (a specifictype of sampling criterion pertaining to trend analyses). In anotherimplementation, an abrupt change in the character of the pixel propertydistribution may be detected by comparing a metric characterizing theproperty distribution with a predicted value of that metric obtained,for example, by exponential smoothing or a moving average of priorsampling property distribution metrics.

FIG. 17 illustrates an exemplary blurring of a background of a digitalimage 1700 using a different sampling trend criterion and anadaptively-sized sampling region. The editing operation shown in FIG. 17is a blurring operation. A small sampling region (not shown) is likelyto result in a slight or undetectable amount of blurring restricted tovery small and separated pixel regions. An adaptive sampling region canexpand the blurring effect to provide detectable results on the texturedbackground.

However, an adaptive sampling region 1702 that is allowed to grow justshort of an abrupt change in the uniformity metric trend (i.e., to 114pixels per side) encompasses pixels exhibiting a much wider pixelproperty distribution. As such, the blur class is wider than for thesmall sampling region. As such, the blurring extends to the boy's leg,which the user perceives as a foreground object as opposed tobackground.

The embodiments of the invention described herein are implemented aslogical steps in one or more computer systems. The logical operations ofthe present invention are implemented (1) as a sequence ofprocessor-implemented steps executing in one or more computer systemsand (2) as interconnected machine modules within one or more computersystems. The implementation is a matter of choice, dependent on theperformance requirements of the computer system implementing theinvention. Accordingly, the logical operations making up the embodimentsof the invention described herein are referred to variously asoperations, steps, objects, or modules. In addition, data structures maybe represented by individual objects, defined data structures,individual database tables, or combinations of associated databasetables. A data field of a data structure may be represented orreferenced by one or more associated database table fields.

The above specification, examples and data provide a completedescription of the structure and use of exemplary embodiments of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

1. A method comprising: sampling pixels in a first region within a toolimpression in a digital image to determine a first distribution of apixel property of the pixels in the first region using a processingunit; modifying the first region within the tool impression to encompassa set of additional pixels within the tool impression; determining asecond distribution of the pixel property based on the pixels in themodified first region using the processing unit; sampling pixels in asecond region within the tool impression to determine a thirddistribution of the pixel property of the pixels in the second regionusing the processing unit; and editing at least one pixel within thetool impression based on the second and third distributions.
 2. Themethod of claim 1 wherein the modifying operation is limited by asampling criterion.
 3. The method of claim 1 wherein the modifyingoperation is limited by a detection of an abrupt change in a pixelproperty trend within the first region.
 4. The method of claim 1 whereinthe modifying operation is limited by a sampling criterion based on auniformity metric.
 5. The method of claim 1 wherein the modifyingoperation is limited by a sampling criterion based on a pixel propertytrend in the first region.
 6. The method of claim 1 wherein themodifying operation is limited by a sampling criterion based on a trendin a measure of variability of a pixel property in the first region. 7.The method of claim 1 wherein the modifying operation is limited by asampling criterion based on a uniformity metric trend in the firstregion.
 8. The method of claim 1 wherein the first distribution ischaracterized by a measure of variability and a measure of centraltendency of pixel property difference, and the ratio of the measure ofvariability and the measure of central tendency of the pixel propertydifference is less than a defined threshold.
 9. The method of claim 1wherein the second distribution is characterized by a measure ofvariability and a measure of central tendency of pixel propertydifference and the ratio of the measure of variability and the measureof central tendency of pixel property difference is less than a definedthreshold.
 10. The method of claim 1 wherein the first region has anarea and the modifying operation comprises: increasing the area of thefirst region by one or more pixels to generate the modified firstregion.
 11. The method of claim 1 wherein the first region has aperiphery and the modifying operation comprises: modifying the peripheryof the first region uniformly to generate the modified first region. 12.The method of claim 1 wherein the first region has a periphery and themodifying operation comprises: modifying the periphery of the firstregion non-uniformly to generate the modified first region.
 13. Themethod of claim 1 wherein the first region has a periphery and themodifying operation comprises: modifying the periphery of the firstregion uniformly in stages to generate the modified first region until adistribution of the pixel property of the set of pixels encompassed bythe modified first region is no longer substantially uniform; andreverting to the modified first region of a previous stage in which thedistribution of the pixel property of the set of pixels encompassed bythe modified first region is substantially uniform.
 14. The method ofclaim 1 wherein the first region has a periphery and the modifyingoperation comprises: modifying the periphery of the first regionnon-uniformly in stages to generate the modified first region until adistribution of the pixel property of the set of pixels encompassed bythe modified first region is no longer substantially uniform; andreverting to the modified first region of a previous stage in which thedistribution of the pixel property of the set of pixels encompassed bythe modified first region is substantially uniform.
 15. The method ofclaim 1 wherein the first region has a periphery that defines an areaand the modifying operation comprises: growing the area of the firstregion to generate the modified first region.
 16. The method of claim 1wherein the first region has a periphery that defines an area and themodifying operation comprises: growing the area of the first regionwithout violating a sampling criterion to generate the modified firstregion.
 17. A computer readable medium encoding a computer program forexecuting on a computer system a computer process, the computer processcomprising: sampling pixels in a first region within a tool impressionin a digital image to determine a first distribution of a pixel propertyof the pixels in the first region; modifying the first region within thetool impression to encompass a set of additional pixels within the toolimpression; determining a second distribution of the pixel propertybased on the pixels in the modified first region; sampling pixels in asecond region within the tool impression to determine a thirddistribution of the pixel property of the pixels in the second region;and editing at least one pixel within the tool impression based on thesecond and third distributions.
 18. The computer readable medium ofclaim 17 wherein the modifying operation is limited by a samplingcriterion.
 19. The computer readable medium of claim 17 wherein themodifying operation is limited by a detection of an abrupt change in apixel property trend within the first region.
 20. The computer readablemedium of claim 17 wherein the modifying operation is limited by asampling criterion based on a uniformity metric.
 21. The computerreadable medium of claim 17 wherein the modifying operation is limitedby a sampling criterion based on a pixel property trend in the firstregion.
 22. The computer readable medium of claim 17 wherein themodifying operation is limited by a sampling criterion based on a trendin a measure of variability of a pixel property in the first region. 23.The computer readable medium of claim 17 wherein the modifying operationis limited by a sampling criterion based on a uniformity metric trend inthe first region.
 24. The computer readable medium of claim 17 whereinthe first distribution is characterized by a measure of variability anda measure of central tendency of pixel property difference, and theratio of the measure of variability and the measure of central tendencyof the pixel property difference is less than a defined threshold. 25.The computer readable medium of claim 17 wherein the second distributionis characterized by a measure of variability and a measure of centraltendency of pixel property difference and the ratio of the measure ofvariability and the measure of central tendency of pixel propertydifference is less than a defined threshold.
 26. The computer readablemedium of claim 17 wherein the first region has an area and themodifying operation comprises: increasing the area of the first regionby one or more pixels to generate the modified first region.
 27. Thecomputer readable medium of claim 17 wherein the first region has aperiphery and the modifying operation comprises: modifying the peripheryof the first region uniformly to generate the modified first region. 28.The computer readable medium of claim 17 wherein the first region has aperiphery and the modifying operation comprises: modifying the peripheryof the first region non-uniformly to generate the modified first region.29. The computer readable medium of claim 17 wherein the first regionhas a periphery and the modifying operation comprises: modifying theperiphery of the first region uniformly in stages to generate themodified first region until a distribution of the pixel property of theset of pixels encompassed by the modified first region is no longersubstantially uniform; and reverting to the modified first region of aprevious stage in which the distribution of the pixel property of theset of pixels encompassed by the modified first region is substantiallyuniform.
 30. The computer readable medium of claim 17 wherein the firstregion has a periphery and the modifying operation comprises: modifyingthe periphery of the first region non-uniformly in stages to generatethe modified first region until a distribution of the pixel property ofthe set of pixels encompassed by the modified first region is no longersubstantially uniform; and reverting to the modified first region of aprevious stage in which the distribution of the pixel property of theset of pixels encompassed by the modified first region is substantiallyuniform.
 31. The computer readable medium of claim 17 wherein the firstregion has a periphery that defines an area and the modifying operationcomprises: growing the area of the first region to generate the modifiedfirst region.
 32. The computer readable medium of claim 17 wherein thefirst region has a periphery that defines an area and the modifyingoperation comprises: growing the area of the first region withoutviolating a sampling criterion to generate the modified first region.33. A computer-readable medium encoding a computer program for executionon a computer system, the computer program comprising: a region samplingmodule that samples pixels in a first region within a tool impression ina digital image to determine a first distribution of a pixel property ofthe pixels in the first region and samples pixels in a second regionwithin the tool impression to determine a second distribution of thepixel property of the pixels in the second region; an adaptive samplingregion module that modifies the first region within the tool impressionto encompass a set of additional pixels within the tool impression anddetermines a third distribution of the pixel property based on thepixels in the modified first region; and an editing module that edits atleast one pixel within the tool impression based on the second and thirddistributions.
 34. The computer readable medium of claim 33 wherein thefirst region has a periphery and the adaptive sampling region modulefurther modifies the periphery of the first region uniformly in stagesto generate the modified first region until a distribution of the pixelproperty of the set of pixels encompassed by the modified first regionis no longer substantially uniform, and reverts to the modified firstregion of a previous stage in which the distribution of the pixelproperty of the set of pixels encompassed by the modified first regionis substantially uniform.
 35. A system comprising: means for samplingpixels in a first region within a tool impression in a digital image todetermine a first distribution of a pixel property of the pixels in thefirst region; means for modifying the first region within the toolimpression to encompass a set of additional pixels within the toolimpression; means for determining a second distribution of the pixelproperty based on the pixels in the modified first region; means forsampling pixels in a second region within the tool impression todetermine a third distribution of the pixel property of the pixels inthe second region; and means for editing at least one pixel within thetool impression based on the second and third distributions.
 36. Thesystem of claim 35 wherein the first region has a periphery and themeans for modifying comprise: means for modifying the periphery of thefirst region in stages to generate the modified first region until adistribution of the pixel property of the set of pixels encompassed bythe modified first region is no longer substantially uniform; and meansfor reverting to the modified first region of a previous stage in whichthe distribution of the pixel property of the set of pixels encompassedby the modified first region is substantially uniform.